1. Field of the Invention
The present invention is directed to the field of medicinal injectors, and, more particularly, to needleless injectors which have spring-actuated pistons which force medicinal fluids through the skin without piercing the skin.
2. Description of the Related Art
Many systems have been developed for injecting liquid medications into persons as part of a treatment program, as vaccination against disease, and for other purposes. Many such medications are injected into the tissues under the skin rather than directly into a blood vessel. The medications thus injected are then absorbed by the circulatory system and transported throughout the body. Such intramuscular injections are used, for example, in the treatment of diabetes. Typically, an injection is made using a hypodermic syringe having a needle which pierces the skin so that the medication forced from the syringe is injected into the underlying tissue.
For many persons, the very thought of receiving an injection in this manner is uncomfortable at best and often frightening. Thus, needleless injectors have been developed to obviate the use of needles. Such needleless injectors apply a high pressure to a medicinal fluid in a syringe to force the fluid out of a small orifice at the end of the syringe. When the orifice of the syringe is held against the skin, the fluid penetrates the skin and enters the underlying tissues where it is absorbed as discussed above.
Various systems for applying the pressure to the fluid in the syringe have been developed. Some needleless injectors have used high pressure gas, such as, for example, carbon dioxide (CO.sub.2). Other injectors have used springs to force the fluid out of the syringe. The present invention is directed to improvements to spring-actuated needleless injectors.